Most days, Mr. Trabocchi works from 9 a.m. to 11 p.m., bouncing among restaurants. His alarm goes off at 5:30 a.m. so he can be at the gym by 6 for a 45-minute training session five days a week. “The busier I am at work, the more important it is to get in my workout,” he says. Mr. Cowie also gave the chef a diet tutorial. “AC told me that the less I ate sugar, carbs and dairy, the less I would crave them, even if I was around them all day at work,” he says. He took a hard look at his diet, cut out baked goods and stopped adding sugar to his espresso.

The Libre is a waterproof button the size of a quarter that sits on the outside of the upper arm. It houses a tiny needle-shaped sensor that rests just under the skin, continuously measuring glucose levels in the interstitial fluid that bathes the cells. Users hold a companion device, or an Android phone, above the sensor to get an immediate reading; an arrow indicates if levels are rising or falling.